Random signal generator



Feb. 3, 1959 NEGRl I 52,72,514

RANDOM SIGNAL GENERATOR Filed Nov. 29, 1955 AMPLIFIER htates ilnite RANDOM SIGNAL GENERATOR Franco Negri, Ivrea, Italy, assignor to lug. C. Glivetti & C., S. p. A., Ivrea, Italy, a corporation of Italy This invention relates mainly to secret telegraph systems and particularly to the full automatic production of a purely random signal sequence for use in enciphering and deciphering permutation code teletypewriter signals.

In a system of secret telegraphy presently known in the art, in connection with which this invention may be used, the enciphered code elements as transmitted are the resultants of the elements of the regular permutation code signals modified by the elements of what is known in the art as a key tape. The key tapes are prepared and supplied to each terminal in advance. The key tapes at each terminal are identical and are operated in synchronism. Each character element of the enciphered code may be made marking or spacing by suitable mechanism, depending upon whether each element of the regular permutation code representing the character and the corresponding element as randomly punched in the key tape are alike or unlike.

Previous proposals for automatically producing random signals have followed two general procedures.

In accordance with one procedure, random signals have been prepared by means of mechanical mixing devices, such as ball boxes or ball mixing machines. Presently known mechanical devices, however, do not in fact produce mathematically random signal sequences and, moreover, such devices generally are complex and expensive to construct.

In accordance with the second procedure, random signals have been prepared by means of electrical devices making use either of acoustical or of electronic noise sources. Generally speaking, such sources are never mathematically random and thus are not adapted to produce perfectly random signal sequences. On the other side, electronic noise sources used heretofore, such as ionized gaseous conductors or conducting vacuum tubes, wherein the random arrival of electrons at the plate produces a so-called shot effect that causes fluctuation about the average value of plate current, require a delicate and highly developed circuity. This to avoid that the shot effect of the vacuum tube, which occurs within a very narrow interval, be biased by external circumstances. I

The invention herein represents an improvement over presently known automatic devices for generating random signals. The generator of this invention is relatively simple and inexpensive to produce and to be operated.

Therefore, the primary object of the invention is the provision of improved means for and methods of generating random signal sequences. Another primary object of the invention is to provide improved means for and methods of producing random key tapes for use in enciphering and deciphering permutation code telegraph signals.

According to the invention I provide a method of generating trains of signal elements having a random sequential arrangement, which is characterized by the feature that each signal element is selectively determined as a function of the number of pulses produced at a given 2,8725 Fatented Feb. 3, 1959 "tee instant by a detector signaling the radiations of a radioactive substance. Therefore, since the radiations of the radio-active substance are absolutely random, the resultant signal sequence will be perfectly random as well.

This and other features of the invention will become apparent from the following detailed description of an embodiment thereof, taken in conjunction with the accompanying drawing.

Referring to the drawing, the reference numeral 1 designates a tape reperforator comprising a line relay 2 and a motor 4. Under the control of trains of impulses sequentially arriving to the line relay 2 through the line 3, the reperforator ll perforates code combinations into a tape 5. The trains of impulses are made up of various permutations of the elements of the five unit code.

The elements of each code permutation are influenced by the radiations of a radio-active substance. This substance, for instance one millionth gram of radium, is shown in the figure by the reference numeral 6 and is suitably contained in a lead case. The radiations of the substance 6 are captured by a detector 7, for instance a Geiger-Muller tube, which signals the presence of a radiation by generating a pulse. These pulses are amplified by an amplifier 8, which may be, for instance, of the type shown on page of the Handbook of Industrial Electronic Circuits by I. Markus and V. Zeluff, McGraw-Hill 1948. The output of the amplifier 8 is connected to the input of a counter, such as a bistable multivibrator or flip-flop circuit 9 of the known type having two stable states and shown, by way of example,

in Fig. 32 (page 15) of the book High-speed Computing Devices, staff of E. R. A., McGraw-Hill 1950. Each pulse from the detector 7 triggers the flip-flop 9, thus energizing either the positive output line 11 or the negative output line 12 of the flip-flop.

The flip-flop 9 is cyclically sensed at predetermined intervals by a rotary distributor generally indicated by the numeral 13. By means of a one-revolution clutch not shown in the drawing, the brush arm 15' of the distributor 13 is adapted to be rotated by a motor 14. The speed at which the arm 15 is rotated corresponds to the speed at which the reperforator 1 is operated by the motor 4.

During each revolution the brush arm 15 senses first a negative start contact 16, then five code contacts 17 and, finally, a positive stop contact 18. The five code contacts 17 are bridged by a common conductor and are connected to the two output lines 11 and 12.

By sensing the flip-flop 9 the distributor 13 is adapted to render it effective to control the impulse permutations to be produced. To this end the brush arm 15 is connected to a generating means, such as a transmitter operable for sending impulse permutations to the reperforator ll, saidtransmitter including a polarized relay 19 controlling the armature of a transmitting contact 20. A locking winding 21 looks the armature of the contact 20 in the position each time assumed according to the polarity of the relay 19.

The extension of each one of the code contacts 17 may be such that the period of time during which an individual contact 17 is sensed by the brush arm 15 be not longer than the average interval between two successive pulses generated by the detector 7. However, if during the sensing of an individual contact 17 the flip-flop 9 is triggered once or more times, after a first fluctuation the energization of the relay 19 stabilizes on the polarity assumed by the contact 17 upon the last triggering of the flip-flop 9.

The mode of operation of the device will now be described.

Each pulse generated by the detector 7 and amplified in 8 triggers the flip-flop 9. Thus the actual state of .erated "by the detector 7. Since the flip-flop 9 operates as a binary counter, the energization of either one of the output lines 11 and 12 depends upon the even or odd number of pulses triggering the flip-flop 9; Upon energization of the output line 11, the code contacts 1'7 are energized positively, and upon energization of the output line 12, the code contacts 17 are energized negatively. During one revolution of the brush arm 15 five impulses each one corresponding to the instant state of the flip-flop 9 Will'thus sequentially be generated. These five code impulses follow the negative start impulse and preceed the positive stop impulse, both impulses being invariably generated by the contacts 16 and 18, respectively, during each revolution of the brush arm 15.

'The trains of. impulses thus generated sequentially energize the relay 19,'controlling the transmitting contact Ztlywhose armature is locked each time in the assumed position by the locking winding 21. The trains of impulses generatedin turn by the transmitting contact 20 are sent through the line 3 to the line relay 2, whereby corresponding code permutations are perforated into the tape-5.

it will thus be apparent that the code permutations making up the key message will depend only upon the time pattern of the radiations captured by the Geiger- Muller tube. Since the time pattern of the radiation of a radio-active substance is absolutely random, the resultant key tape produced by the generator according to the invention will be perfectly random. Since, moreover, the radiation of the radioactive substance is fully unbiased by external influences, the operation of the generator will be of the highest reliability.

It should be remarked that unlike previous attempts of automatic random signal generators, the present generator employs only a single random source, thus making the device of particularly inexpensive manufacture. However, nothing herein prevents from using an individual radio-active source for each one of the elements of the code used. In this case each punch pin of the tape perforator may be directly controlled by an individual con trol chain comprising the radio-active substance, the detector and the flip-flop, the impulse permutations being bodily transferred to the tape perforator in synchronism with the operation of the perforator.

Furthremore, it should be noted that the flip-flop 9 represents only one type of device. for stabilizing either one of two conditions under the control of the pulses produced by the detector 7. A relay or any other suitable locking device may be used instead ofthe flip-flop, the

term bistable multivibrator used in the appended claims referring to all these kinds of devices.

The embodiment of the invention described hereinabove uses bipolar impulses, generated either by positive or negative contacts or by make and break contacts.

Consequently, both cases provide the use of a bistable multivibrator. Should, however, a particular permutation code provide the use of signal elements having three conditions, as, for instance, 0 and impulses, it would be advisable to use. aternary counter instead of the binary counter represented by the bistable multivibrator. In this casethe instant condition'dctermined by the ternary counter will still depend upon the number of pulses produced by said detector and will recur at constant intervals of three pulses instead of two.

From the foregoing description it will be understood that many changes may be made in the above device, and different embodiments of the invention could be made Without departing from the scope thereof. it is, therefore, intended that all matter contained in the above escription, or shown in the accompanying drawing, shall be interpreted. as illustrative, and not in a limiting sense.

What I claim is:

1. In a device for producing random signals made up of binary code elements, the combination of a source of random pulses, 'a flip-flop circuit coupled to said source and responsive to said random pulses sequentially to produce negative and positive output pulses, cyclical distributor means coupled to said flip-flop circuit'to sense the output thereof at predetermined instancs in the course of each cycle to produce a train of binary code pulses each of which is determined by the corresponding output pulse at the instant of sensing, and means to record said train of code pulses.

2.'In a device as set forth in claim 1., wherein said source of random "pulses is constituted by a radio-active substance and 1a Geiger-Muller detector responsive to the radiations of said substance to produce random pulses.

3. In a device for producing key tape for enciphering permutation codetelegraph signals and comprising a tape reperforator and a transmitter operable for sending impulse permutations to said reperforator, the combination of a source of random pulses constituted by a radioactive substance and a detector responsive to the radiations of said substance to produce said random pulses,

a bistable multivibrator' sequentially triggered by said random pulses from saidsource to produce negative and '1' positive output pulses, and a distributor cyclically sensing the output of said multivibrator at predetermined intervals in the course of each cycle to operate said transmitter according to the instant polarity of said output.

References Cited in the file of this patent -UNITED STATES PATENTS 2,539,014 I Frantz 340/1 17 

